Without hard numbers or hard details, evaluating ads requires a bit of guesswork. But we can compare all of that to other industry trends and published research to get a feel.
Battery in a box
Let’s start with two things Tesla claimed to already exist in its pilot production plant: its new cell design and some improvements in manufacturing. Tesla took off using existing and commonly available 18650 cylindrical lithium-ion cells, while most EVs were built with a flat pocket or prismatic cells (more like thin batteries in phones and laptops). In a cylindrical cell, long sheet-like anodes, separators, and cathodes are sandwiched, coiled, and packed in a cylinder-shaped box. The cathode and anode sheets each have a thin “tab” that connects to the positive and negative terminals of the battery box.
One of the best ways to make a battery more energy dense is to get rid of as much packaging as possible. Make the separator super thin and minimize the outer container and battery components, and you will have more electricity stored per kilogram. Obviously, there are limits to what you can shave, so another way to do this is to increase the ratio of battery volume to wrapping area. In other words, make a bigger box.
Tesla did this by introducing the 2170 cell with the Model 3 and Powerwall. This cylinder measured 21 millimeters by 70 millimeters instead of the 18 by 65 dimensions of the 18650 cell. But getting bigger presented challenges to Tesla, as a larger box contains longer rolls and longer rolls mean that the anode and cathode extend further from the tab that connects them to the battery terminals. The longer path for electrons causes problems for safe fast charging and creates more heat which is more difficult to escape.
Tesla’s solution to this, leading to a a lot 4680 cell larger, is a new ‘table-less’ design with contacts running the length of the anode and cathode sheets – forming a rose-shaped gathering at the ends when all wound up – maintaining the length of the electrical path to the terminal runs across the sheet. “Sometimes what’s elegant and simple is still difficult,” said Tesla’s Drew Baglino. “And it took us a lot of tries, but we’re happy where we ended up. ”
“It might sound a little silly to some people,” Musk added, “ [but] for people who really know cells, this is a major breakthrough. “
It’s really hard to know exactly how this compares to cells used in other EVs, given manufacturers’ secrecy, but it could be that this table-less design validates Tesla’s choice to stick with the shape. cylindrical cell.
The other half of making a new type of cell is designing the machines that make it. As detailed in our companion’s story, Tesla found ways to dramatically increase the throughput of parts of the battery line. The tablet-free design actually helps with this, as the electrode sheet can just keep flying through the rollers. And with other changes we’ll get to in a moment, they’re talking about increasing production while using less plant floor space and less energy. This will help them meet their cost reduction goals and increase their production goals.
Pack it up, pack it up
An EV doesn’t run on a battery cell, of course, but rather on a battery pack full of cells. There’s a lot going on in these batteries including charge management, cooling, and fire safety measures. This makes the engineering of the pack very relevant for the global the energy density of the vehicle’s storage, and therefore its range.
Tesla described a new pack design that reduces some of the structural support, which means more cells in less volume. And since that involves a redesigned pack that also serves as the structure for the vehicle, it likely has cost advantages at the vehicle level as well.
This pack design probably exists, but there was no word on which vehicles it will go in. Could production switch to an existing vehicle, or is this design just part of the Cybertruck, the Tesla Semi, or an unnamed $ 25,000 vehicle? Musk didn’t say it.
But he fact have a lot to say about the chemistry of new battery cells. And this is where the deadlines become more blurry. New chemistries for the anode and cathode were discussed – both would innovate.
The anode of modern lithium-ion batteries is made of graphite. The structure of graphite allows it to host the lithium atoms that travel to the anode during charge, but that’s all it does. This means that a substantial part of the volume and weight of the cell does not directly contribute to energy storage beyond just keeping the thing running. If you could lose bulk and weight there, the energy density of the cell would increase.
Tesla and some other manufacturers are currently adding a little silicon inside this graphite, as it allows the same volume of anode to hold more lithium. A significantly better (and cheaper) option would be the use of pure silicon. But while graphite allows lithium to come in and out without changing shape, silicon has a bad habit of expanding as it charges with lithium. This creates structural failures in the silicon, degradation of performance over time, and potentially dangerous cell failures. container.
There is a lot of research on alternative anodes for lithium-ion batteries, but none has yet reached the market. Tesla claims to have designed an anode with tiny particles of silicon in a conductive and elastic polymer. This allows for a durable and safe silicon anode cell, he says, which would be a big deal.
This cell comes with a reported cost reduction of about $ 10 per kilowatt hour for silicon in graphite to over $ 1 per kilowatt hour for pure silicon. When it comes to the range of vehicles, the company claims a 20% improvement. But no other property (like longevity over its current anode) has been described, so it’s not clear if Tesla is ready to put it in a battery and sell it. today. (Although for what it’s worth, it doesn’t sound too different from an anode material Sila Nano – a company with Tesla alumni – says it will start supplying batteries for electronics this year.)
Tesla also switches to (slightly) different chemistries on the cathode side. And yes it is plural chemistries, which is at least as remarkable as the chemical details. Tesla now wants to supply three different types of lithium-ion batteries, ranging from the most economical to I give it all it has to the captain.
Tesla currently uses NCA (i.e. lithium-nickel-cobalt-aluminum) chemistries, while lithium-nickel-manganese-cobalt (NMC) chemistries are common in the rest of the electric vehicle industry. Cobalt is the most expensive of these elements, and most of it comes from mines in the Democratic Republic of the Congo, where unsafe working conditions and child labor are serious concerns. As a result, the industry has tried to reduce the use of cobalt.